[Python-Dev] Python startup time

[Cesare Di Mauro]

2017-07-21 4:52 GMT+02:00 Nick Coghlan <ncoghlan at gmail.com>:

> On 21 July 2017 at 12:44, Nick Coghlan <ncoghlan at gmail.com> wrote:
> > We can separately measure the cost of unmarshalling the code object:
> >
> > $ python3 -m perf timeit -s "import typing; from marshal import loads;
> from
> > importlib.util import cache_from_source; cache =
> > cache_from_source(typing.__file__); data = open(cache,
> 'rb').read()[12:]"
> > "loads(data)"
> > .....................
> > Mean +- std dev: 286 us +- 4 us
>
> Slight adjustment here, as the cost of locating the cached bytecode
> and reading it from disk should really be accounted for in each
> iteration:
>
> $ python3 -m perf timeit -s "import typing; from marshal import loads;
> from importlib.util import cache_from_source" "cache =
> cache_from_source(typing.__spec__.origin); data = open(cache,
> 'rb').read()[12:]; loads(data)"
> .....................
> Mean +- std dev: 337 us +- 8 us
>
> That will have a bigger impact when loading from spinning disk or a
> network drive, but it's fairly negligible when loading from a local
> SSD or an already primed filesystem cache.
>
> Cheers,
> Nick.
>
> --
> Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
>
Thanks for your tests, Nick. It's quite evident that the marshal code
cannot improve the situation, so I regret from my proposal.

I took a look at the typing module, and there are some small things that
can be optimized, but it'll not change the overall situation unfortunately.

Code execution can be improved. :) However, it requires a massive amount of
time experimenting...

Bests,
Cesare

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